The Drake Equation is that famous equation where you count how many stars there are, figure out the chance of a star having planets, of planets having water, etc. etc. until finally you get some rough estimate of the chance of live evolving elsewhere in the universe. It’s a little more complicated (and also simpler) than that, but one factor that permeates the equation is the life-friendliness of a star system. It might turn out that the presence of asteroid belts affects life-friendliness. NASA reports some new research indicating…

…that the size and location of an asteroid belt, shaped by the evolution of the sun’s planet-forming disk and by the gravitational influence of a nearby giant Jupiter-like planet, may determine whether complex life will evolve on an Earth-like planet.

This might sound surprising because asteroids are considered a nuisance due to their potential to impact Earth and trigger mass extinctions. But an emerging view proposes that asteroid collisions with planets may provide a boost to the birth and evolution of complex life.

Asteroids may have delivered water and organic compounds to the early Earth. According to the theory of punctuated equilibrium, occasional asteroid impacts might accelerate the rate of biological evolution by disrupting a planet’s environment to the point where species must try new adaptation strategies.

Apparently, very few planetary systems are expected to have Jupiter-like planets in the right position to make the right size asteroid belts in the right place, so a rocky planet can get things like water. The researchers,

…Martin and Livio suggest that the location of an asteroid belt relative to a Jupiter-like planet is not an accident. The asteroid belt in our solar system, located between Mars and Jupiter, is a region of millions of space rocks that sits near the “snow line,” which marks the border of a cold region where volatile material such as water ice is far enough from the sun to remain intact. When Jupiter formed just beyond the snow line, its powerful gravity prevented nearby material inside its orbit from coalescing and building planets.

Instead, Jupiter’s influence caused the material to collide and break apart. These fragmented rocks settled into an asteroid belt around the sun.

“To have such ideal conditions you need a giant planet like Jupiter that is just outside the asteroid belt [and] that migrated a little bit, but not through the belt,” Livio explained. “If a large planet like Jupiter migrates through the belt, it would scatter the material. If, on the other hand, a large planet did not migrate at all, that, too, is not good because the asteroid belt would be too massive. There would be so much bombardment from asteroids that life may never evolve.”

…

“Based on our scenario, we should concentrate our efforts to look for complex life in systems that have a giant planet outside of the snow line,” Livio said.

Comments

[…] The Drake Equation is that famous equation where you count how many stars there are, figure out the chance of a star having planets, of planets having water, etc. etc. until finally you get some rough estimate of the chance of live evolving elsewhere in the universe. It’s a little more complicated (… http://scienceblogs.com/&#8230; […]

I’m not a scientist, but I simply do not and cannot understand how any rational person could assert either that, in the entire known universe, life of any kind has developed only once on this spec of dust – or that if life exists elsewhere it must have developed on the same type of planet or solar system. Moreover I would be deeply disappointed to discover that anything as flawed as DNA/RNA would be the universal basis for life.

The aspect of the paper that is being trumpeted as significant is gratuitously speculative and based on selection bias. Only 4% of known giant planets are outside of the snow line because of bias, nothing more. I can’t accept this assumption or the anthropic bias inherent to this general kind of reasoning. It’s an otherwise unremarkable paper getting undeserved hype.

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